A critical need exists for a dosage form for delivering an aqueous soluble or an aqueous insoluble drug orally to a patient in one or two doses per day to assure constant availability of drug. The need exists for a dosage form for delivering an aqueous soluble drug because (1) aqueous soluble drugs are difficult to formulate into a dosage form, such as an osmotic dosage form, and because (2) aqueous soluble drugs often are prematurely released from the dosage form by unwanted diffusion, or by interaction with a fluid in a gastrointestinal environment, thereby extracting the drug from the dosage form. The need exists for a dosage form for delivering an aqueous insoluble drug because (3) aqueous insoluble drugs are difficult to delivery from a dosage form, such as an osmotic dosage form, as these drugs lack the kinetic ability to develop an osmotic pressure gradient, and because (4) aqueous insoluble drugs are delivered as intact solid forms and they may cause irritation of the mucosa of the gastrointestinal tract.
In the light of the above presentation it will be appreciated by those versed in the dispensing arts to which this invention pertains that a critical need exists for, (5) a dosage form that can deliver both soluble and insoluble aqueous drugs at a controlled rate to provide a dosage, therapeutic administration of drug in either instance for its beneficial effects over a prolonged time span, and for (6) a dosage form that can administer a drug essentially independent of its chemical properties. It will be further appreciated by those versed in the medical art that a novel and unique dosage form that can administer such a drug at a controlled rate over time, and simultaneously provide substantial therapy, would represent an advancement and a valuable contribution to the art.